Antarctic Ecosystem: Seasons

The Seasons
Because of the earth's tilt and orbit around the sun, the poles receive less energy and heat from the sun. This results in only two polar two seasons—summer and winter. In summer at the poles, the sun does not set, and in winter the sun does not rise. Expedition 10 takes place close to the South Pole, in the ocean around Antarctica during the southern hemisphere summer season. The days will be very long, with the sun below the horizon for only a few hours a day, and the sky will not become completely dark at night.

Antarctic summer after sundown
November—The sun had set one hour before this photograph was taken at 1:30 am. It rose again around 2:30 am. At this time of year, it doesn't get "dark" but twilight is spectacular! (Photo by Regina Campbell-Malone)

These dramatic seasonal variations control the ecosystem, and, as a result, Southern Ocean sea life faces challenging conditions. Ice forms in winter over much of the sea around Antarctica, and rapidly retreats in the spring when the ice melts. Summer is a season of long days and slightly warmer temperatures when phytoplanktonsmall or microscopic photosynthetic organisms that float or drift in great numbers in fresh or salt water near the surface and are the base of the ocean food chain can grow rapidly and produce food for the entire ecosystem. High winds blowing from the continent mix the seawater, bringing high levels of nutrients necessary for phytoplankton growth near the sea surface, where there is sunlight.

Earth’s Tilt
The Earth is slightly tilted—that is what gives us our seasons.

Here’s how it works. On one side of its orbit around the sun, the Earth is tilted towards the sun. During this time, the northern hemisphere receives more heat so has higher temperatures—it is summer. Six months later, the Earth is on the other side of its orbit, and the Earth is tilted away from the sun. Now, the northern hemisphere receives less heat so it is colder—it is winter.